running electrics to garden room

RobAMerc

hi,

I am building a garden room.

I have had 2 electricians in and got differing information.

Its a long run - 55 meters
Its not going to be using anything too heavy - 4 sockets, 6 downlights

My intention is to run the cables myself and have the sparky wire it to the mains

I want to

1. new consumer board
2. run SWA along the wall - the way the wall is built there is a cavity between mine and next door neighbours - much lower on my side, I can hide the cable in the cavity
3. 4 sockets - "first fix" wired by me - 2.5 mm2 twin earth cable less than 10m
4. 6 LED downlights
5. 1 outside light
6. underfloor electrical heating - 6sqm

how does this sound ? is 4mm2 enough cable ?
do I need SWA ?

thanks

Car99

Have you a sparky that's happy to let you do some of the wiring?

RobAMerc

talked to 2 - both happy to let me do the grunt work

one suggested SWA - buried - other said NYMJ in the cavity is fine

I'm confused

2011

RobAMerc wrote: »

talked to 2 - both happy to let me do the grunt work

one suggested SWA - buried - other said NYMJ in the cavity is fine

I'm confused

NYMJ is not UV resistant as such should not be exposed to sunlight. It is really an indoor cable that can only be used outside when installed in cable containment.

Burying the SWA would be my preference.

The cable size would depend mainly on load size and length of run. Regarding underfloor heating, how many kW?

RobAMerc

2011 wrote: »

NYMJ is not UV resistant as such should not be exposed to sunlight. It is really an indoor cable that can only be used outside when installed in cable containment.

Burying the SWA would be my preference.

The cable size would depend mainly on load size and length of run. Regarding underfloor heating, how many kW?

Thanks - this is Underfloor Mats I was thinking about.
Its the main load I would imagine - otherwise it wouldnt be much more than a telly or laptop, but its 50m from main consumer board.

I'd personally be oversizing the cable,you never know what you might want to add from the new CU.

2011

BrownFinger wrote: »

I'd personally be oversizing the cable,you never know what you might want to add from the new CU.

So would I.
3 x 6 mm sq. SWA at least.

The length of the cabe run is also important.

Underfloor heating = 900W
Lighting allow 100W
Sockets allow 5000W (depends on the use of the room) - I would protect these with a 16 A B type RCBO.

Total = 6 kW, so allow 26 amps

Personally I would not go for electric underfloor heating. Once the element fails (always happens) it is impossible to replace without major upheaval. Also regardless of what the salesman says it will not work under a wooden floor or carpet. Also it has a very slow response time.

2011

I forgot to say I would also allow at least 20% for future.
So 26 +20%, allow 32 amps. So it looks like a 6mm sq. cable at least.

GreeBo

+1 on avoiding devi mat type heating. It will only work on tiled etc flooring which makes repair a disaster and means it's freezing when not on.
Assuming it's a single room, 1 or even 2 convection heaters will be fine and have fast response times and can be thermostatically controlled for comfort.

RobAMerc

Thanks for the advice on underfloor, i will give it a miss. So 6mm swa - ok to run it in cavity ?
Its way more likely to get chopped if i buty it i think.

Best place to buy this stuff online?

Thanks for the help.

2011

RobAMerc wrote: »

Thanks for the advice on underfloor, i will give it a miss. So 6mm swa - ok to run it in cavity ?

SWA is ok in a cavity. So is the cheaper NYMJ once sufficient mechanical protection is provided in addition to shielding from sunlight.

Regarding the size of the cable:
1) The length of run will be a factor.
2) The rating and type of protective device will be a factor.
3) The load will be a factor, I only took a guess at this load size. I have no idea what the socket loading will really be or what the new heating load will be.

So a proper sizing exercise will need to be carried out. Most likely a 6 sq. will be sufficient, but it is impossible to provide a definitive answer with the limited information provided.

As already stated it would be better to bury the cable. I would also run Ethernet cabling (such as CAT6). This would be so much better that trying to rely on wireless.

It is always bets not to buy the cabling. You will just pay more and be charged a higher VAT rate. Also you are then responsible for measuring the run. Most REC's will pull the cable off a drum and cut it exactly to length (without any waste).

When I was a REC customers constantly provided me with low quality expensive materials that were not fit for purpose. It was very frustrating. I ended up avoiding dealing with these people as it was not worth the hassle. There is too much work around to bother with the lost time from installing poor quality kit. It also resulted in a disappointed customer.

For the record I don't do any installation work anymore (apart from family).

Bruthal

55 meters, id be looking at 10 square myself unless its only ever going to be 2 or 3 sockets and light for storing the lawnmower. Smaller intended loads likely end up bigger. All depends on the loading of course. Min 6 square anyway.

SWA cable is the one for this.

2011

Bruthal wrote: »

55 meters, id be looking at 10 square myself unless its only ever going to be 2 or 3 sockets and light for storing the lawnmower. Smaller intended loads likely end up bigger. All depends on the loading of course. Min 6 square anyway.

SWA cable is the one for this.

My bad, I missed the 55m in the 1st post.

Yeah, I would think at least 10mm sq. I would take a close look at the loading to reduce cable size as this will be very expensive.

Wiring the sockets and heaters in 4 mm sq. may reduce overall costs if it allows for a smaller SWA. If well insulated perhaps one heater would be sufficient, this may also help.

GreeBo

If he wants to do as much work as possible, would it make sense to do the digging and bury some conduit, that way the SWA and any other cables can be pulled though.
(+1) on a data cable, your garden room is probably going to become a home office.

punisher5112

I'd run the ESB red conduit and leave a rope in it if ever needed extra.

RobAMerc

50m of 10mm2 armoured cable is 450 from screwfix - thats €450 to run a laptop and some light bulbs!

I understand some of the suggestions here are helping me future proof the job, but given that I am unlikely to be trying to launch the space shuttle from there any time soon - is this not a bit much ?

2011

RobAMerc wrote: »

50m of 10mm2 armoured cable is 450 from screwfix - thats €450 to run a laptop and some light bulbs!

Now you are asking for something entirely different.
Is there no longer a heating load?
Have you removed the sockets?

If so you could get away with a far smaller cable by installing just one spur outlet for the laptop, a few LEDS, no sockets, no electric heating and no future allowance.

GreeBo

RobAMerc wrote: »

50m of 10mm2 armoured cable is 450 from screwfix - thats €450 to run a laptop and some light bulbs!

I understand some of the suggestions here are helping me future proof the job, but given that I am unlikely to be trying to launch the space shuttle from there any time soon - is this not a bit much ?

50M is s significant distance though.

If you don't really know what you want to be in the room and want to save money, I would run conduit (esb or otherwise) and go with 6mm2 and a limited number of sockets.

If in future you can pull through another 6mm2 if you need another ring/etc (though depending on the makeup of the room this might cause disturbance, so potentially wire two circuits now but only connect one to the DB.)

Note that this will increase the costs at the DB since you will effectively need 2 of them.
/edit
Actually is that true? Would you connect both 6mm2 to the same breakers and upgrade the breaker? Wouldnt that leave you vulnerable if one cable was damaged since all current would flow through the other one? I'm sure the regs cover it!

Bruthal

RobAMerc wrote: »

50m of 10mm2 armoured cable is 450 from screwfix - thats €450 to run a laptop and some light bulbs!

Well it might be €200 less if you looked in electrical shops.

But besides that, why not use the laptop in the house where it will be warm.

Bruthal

2011 wrote: »

Now you are asking for something entirely different.
Is there no longer a heating load?
Have you removed the sockets?

If so you could get away with a far smaller cable by installing just one spur outlet for the laptop, a few LEDS, no sockets, no electric heating and no future allowance.

And no DB needed. 2.5 swa straight to a socket, plug in a light.

2011

GreeBo wrote: »

50M is s significant distance though.

It is and I also see that it has reduced from 55m in the first post

We also need to consider the the volt drop calculation has to start at the point of supply and finish at the final connection point. In this case from the ESB meter all the way to the socket outlet / spur outlet / light fitting in the garden room. So it will be more than 50m.

GreeBo

2011 wrote: »

It is and I also see that it has reduced from 55m in the first post

We also need to consider the the volt drop calculation has to start at the point of supply and finish at the final connection point. In this case from the ESB meter all the way to the socket outlet / spur outlet / light fitting in the garden room. So it will be more than 50m.

If it keeps up at the same rate soon it will be an extension and all these problems go away!


I'm assuming the 50(55)M is from the existing DB to the new DB and that the room isnt big enough to have to worry about any additional drop around it but its a good point and could add another 10m+ its the measurement is just from building to building.

Bruthal

GreeBo wrote: »

Note that this will increase the costs at the DB since you will effectively need 2 of them.
/edit
Actually is that true? Would you connect both 6mm2 to the same breakers and upgrade the breaker? Wouldnt that leave you vulnerable if one cable was damaged since all current would flow through the other one? I'm sure the regs cover it!

6 square mains circuits wouldnt be run in parallel to make up for using the next size up.

It is regularly done if for example a 4x240 was required, 2 of 4x120s can be used instead. But small sizes would not be installed this way.

RobAMerc

2011 wrote: »

Now you are asking for something entirely different.
Is there no longer a heating load?
Have you removed the sockets?

If so you could get away with a far smaller cable by installing just one spur outlet for the laptop, a few LEDS, no sockets, no electric heating and no future allowance.

I was being facetious - I wasnt re-speccing the job, I hope I wouldnt have to re-iterate the whole thing every time I am remarking about it !

Bruthal wrote: »

Well it might be €200 less if you looked in electrical shops.

But besides that, why not use the laptop in the house where it will be warm.

Is this after hours ?
Well I did post early on asking where best to buy it.

2011 wrote: »

It is and I also see that it has reduced from 55m in the first post

again ye know the spec at this stage.

Bruthal

RobAMerc wrote: »

Is this after hours ?

I suppose sometimes, when asking for advice on cable size, the recommendations dont suit. Good luck with it.

JL spark

Bruthal wrote: »

I suppose sometimes, when asking for advice on cable size, the recommendations dont suit. Good luck with it.

Use at least 10ml cable , your final ze test could be too high on a 6ml , plus my two cents worth , I’d never connect up someone else’s work like that , don’t think any decent spark would , plus your not permitted to run circuits any way , whole job has to be under taken by a REC ,
What age is your main property ? And is consumer unit able to take this new load ?

Bruthal

JL spark wrote: »

Use at least 10ml cable , your final ze test could be too high on a 6ml

It depends. A long run with 6 square might have a 20 amp mcb If the size is purely for a long length.

lockdownrescue

punisher5112 wrote: »

I'd run the ESB red conduit and leave a rope in it if ever needed extra.

Sorry dont want to hijack this thread but are you allowed run multiple cables in a red duct?

RobAMerc

Bruthal wrote: »

But besides that, why not use the laptop in the house where it will be warm.

RobAMerc wrote: »

Is this after hours ?

Bruthal wrote: »

I suppose sometimes, when asking for advice on cable size, the recommendations dont suit. Good luck with it.

I asked about cable for a garden room, you suggested I stay in the house - and you are suggesting I dont deserve help because I asked about the relevance of your response ?

RobAMerc

JL spark wrote: »

What age is your main property ? And is consumer unit able to take this new load ?

Really ?
Are you saying that as a competent DIYer I am unable to dig a trench and run some wire in it ? As the builder of a timber construction "house" for all intents and purposes, I am deemed incapable of drilling some holes in my frame and threading some wire through it - and that regs stop any sparky having spec'd, directed and then assessed the work to wire that into the main consumer board and then sign off?

I am honestly in total shock :eek: - I was able to help my friend build his own light aircraft and I have recently rebuilt the brakes on my car - the plane was deemed fit to fly after and inspection and the car passed the nct !

JL spark wrote: »

What age is your main property ? And is consumer unit able to take this new load ?

All the electrics in the house are less than 5 years old - (done by a REC )

Bruthal

RobAMerc wrote: »

I asked about cable for a garden room, you suggested I stay in the house - and you are suggesting I dont deserve help because I asked about the relevance of your response ?

Told you 10 square based on first post. You didnt like that recommendation. Mystic meg will be of more help now I think based on later posts.